What is the reason (NOT REASONING (guessing/speculating)!) that you have to be friend with someone for at least three days to receive a gift?
Put some money on my main battle.net account to buy a 2nd license of D3 (the current spring sale of the eternal collection) and install it on another laptop.
Doesn’t work. Get the “nice” message that I already have that; well, I know that…
Then tried to gift it to one older account that I only used a while to play the free bit of Diablo 3 for testing purposes. So I became my own friend after I accepted the invite from myself… 
Then this: Blizzard Support - You Haven’t Been Friends Long Enough (battle.net).
Now have to wait for some more month for another sale… … … 